By the time I started to learn to drive buses, with Crosville in 1985, a bus driver’s left foot had little to do, except perhaps to give a sticking cab door a kick at the end of a shift. Certainly in the region in which I was working, buses didn’t have clutch pedals. The gearboxes were mostly semi-automatic and new buses were coming with horrible fully-automatic boxes that took the decision to change gear out of the driver’s hands altogether.
Nevertheless, the thinking at Crosville at the time was to use venerable Bristol Lodekkas with “crash” gearboxes to train drivers, since if you can drive one of those you should be able to drive anything. The mystery of the crash gearbox is very easily resolved. To stop the gears making an awful crunching noise you have to listen to the engine sound and just as the engine is revving at the right speed for the next gear, foot down on the clutch and shift the gear lever just at the same time as the foot is going down.
Changing up the gears is straightforward enough… clutch down, release gear, wait for revs to die, then clutch/select next gear in one co-ordinated move. The tricky bit is changing down where, once the gear is in neutral, the engine needs to be faster to change down, so has to be revved up, but just the right amount for the particular road speed in that gear. It takes a little while to get the hang of it but you get an ear for it.
Back in the 1960s Bristol Commercial Vehicles, which built almost all the new buses for Crosville in that decade, had a reputation for making life hard on drivers with these crash gearboxes whilst their competitors were fitting their vehicles with synchromesh gears [which could be changed in one go like a manual gearbox in a car] or preselector gearboxes with electric or air-operated selectors. But a new invention came on the market and by 1967 Bristol finally gave companies the option of buying their buses with controls that made life much easier for the driver: the semi-automatic gearbox!
I will deal with this booklet in two parts since the semi-automatic gearbox and combustion heater were two very different things.
The gearbox is described as a very intricate and expensive luxury, to be treated with respect. …
As you can see from these instructions, the gearbox was designed to be changed in a similar procedure to the crash gearbox but without the need for a clutch pedal and without the risk of failure. These gearboxes were tolerant, unlike the manual counterpart which demanded absolute precision. Similarly changing down:
I have to say that I followed this guidance when driving… it wasn’t hard to do. But there were lots, and I mean lots of drivers who realised that the gearboxes were very tolerant of being slammed from one gear to the next with little loss of power in the process and so better acceleration. So pausing between gears on these devices became something of a rarity as the years went on. Sadly that reduced the life of the gearboxes and added to the cost of bus operation through the need to replace gearboxes prematurely. Gearbox abuse was considered such a serious problem by the National Bus Company that they got Tony Bastable in to give the drivers a jolly good ticking off.
I will leave you with a link to that very video all trainees had to sit through, me included, in a room at Sealand Road Works. They Don’t Grow on Trees
And another, the Wikipedia entry for Self-Changing Gears